1. Field of the Invention
This invention relates to a diaphragm for a speaker and, more particularly, to an improvement in a material constituting such a diaphragm.
2. Description of the Prior Art
Greater lightness, larger hardness, and larger internal loss (periodic damping) are requirements in the characteristics of a diaphragm for a speaker. More specificially, the uniform operation of a diaphragm is desired in a frequency range as wide as possible with respect to an input signal in order to reproduce a high fidelity sound by the speaker. Accordingly, it is advantageous for the diaphragm to be lighter and harder. In other words, it is advantageous that the ratio E/.delta. be made larger where E is yound modulous and .delta. is density. Also, the internal loss must be made larger to prevent undesirable resonance.
A conventional diaphragm for a speaker could not satisfy all the desired features sufficiently. For example, although hard paper which was widely in common use had an advantage of lightness, it was inferior in hardness. Also, a light metal such as aluminum, titanium, beryllium, and the like was used as a diaphragm of a tweeter speaker of a small diameter. However, it was required to retain the bending strength across a large area of the diaphragm in order to use the diaphragm as a woofer speaker of a large diameter. Accordingly, the thickness of the diaphragm was required to be increased, thus resulting in an increased mass of the diaphragm as a whole. The increased mass thereof became an obstacle in the use of the light metal such as aluminum, titanium, and the like to a speaker of a large diameter. As a method of applying these light metals to a diaphragm of a speaker of a large diameter, a construction is proposed by Barlow "The Development of a Sandwich Construction Loudspeaker System", Journal of the Audio Engineering Society, June 1970, vol. 18, No. 3. wherein a porous synthetic resin is used as a damping material (core material) and it is held between light metals such as aluminum, and the like. However, such a method does not fully utilize the nature of the metals completely.
Also, in the conventional paper-made diaphragm and metal-made diaphragm, the physical conditions of the materials restrict the design conditions of the speaker unit. Thus, changes in the physical conditions of the diaphragm restrict the free selection and design of the acoustic characteristics.